Miktopolymer compositions

ABSTRACT

The present invention provides a block copolymer composition and method of making the same having the structures (A2-B)n—X-(A1) or (A2-B2)n—X—(B1A1), where A1 and A2 are each a polymer block of a monoalkenyl arene and B, B1, and B2 are each a polymer block of one or more conjugated dienes or a hydrogenated diene polymer, n is an integer from 2 to 30 and X is the residue of a coupling agent.

CROSS REFERENCE TO RELATED APPLICATION

The current application claims the benefit of the earlier priorityfiling date of the provisional application Ser. No. 61/036,117, that wasfiled on Mar. 13, 2008 and the provisional application Ser. No.61/038,449, that was filed on Mar. 21, 2008.

FIELD OF THE INVENTION

The present invention relates generally to novel compositions comprisingdissimilar polymer arms (“miktopolymers”) and the invention relates moregenerally to novel compositions comprising dissimilar polymer arms(“miktopolymers”) comprising (1) anionic block copolymer arms of monoalkenyl arenes and conjugated dienes and (2) mono alkenyl arenehomopolymer arm(s).

BACKGROUND OF THE INVENTION

The preparation of block copolymers is well known. In a representativesynthetic method, an initiator compound is used to start thepolymerization of one monomer. The reaction is allowed to proceed untilall of the monomer is consumed, resulting in a living homopolymer. Tothis living homopolymer is added a second monomer that is chemicallydifferent from the first. The living end of the first polymer serves asthe site for continued polymerization, thereby incorporating the secondmonomer as a distinct block into the linear polymer. The block copolymerso grown is living until terminated.

Termination converts the living end of the block copolymer into anon-propagating species, thereby rendering the polymer non-reactivetoward monomer or coupling agent. A polymer so terminated is commonlyreferred to as a diblock copolymer. If the polymer is not terminated theliving block copolymers can be reacted with additional monomer to form asequential linear tri-block copolymer. Alternatively the living blockcopolymer can be contacted with multifunctional agents commonly referredto as coupling agents. Coupling two of the living ends together resultsin a linear triblock copolymer having twice the molecular weight of thestarting, living, diblock copolymer. Coupling more than two of theliving diblock copolymer regions results in a radial block copolymerarchitecture having at least three arms.

One of the first patents on linear ABA block copolymers made withstyrene and butadiene is U.S. Pat. No. 3,149,182. Various blockcopolymers and processes for making them have been proposed over theyears. Studies of such polymers and their morphology in the past haveshown that normally there is a phase transition from a sphericalmorphology to a cylindrical morphology at about 17 wt. % styrene andcylindrical to lamellar morphology at about 32 wt. % styrene. Whilespherical and cylindrical morphologies still have a continuous rubbermatrix that makes them soft and elastic, lamellar morphologies arecontinuous in both the elastic and rigid phases, thus becoming aplastic. This means that it has not been possible in the past to obtaina truly elastomeric block copolymer having a styrene content of as highas 70 wt. %. In the past, block copolymers with styrene contents greaterthan about 35 wt. % were merely high impact polystyrene plastics. Higherstyrene content block copolymer elastomers have been made by dispersingstyrene monomers in the elastomer phase, but these increase the glasstransition temperature (Tg) of the elastomer and represent syntheticchallenges in manufacturing.

Theoretical [S. T. Milner, Macromolecules 27, 2333-2335 (1994).] andexperimental [D. J. Pochan et. al., Macromolecules 29, 5091-5098 (1996)]investigations have been reported in the literature on star-shaped blockcopolymers of the structure S—X—(B)_(n), i.e. one polymer block ofpolystyrene connected to n polymer blocks of type B (polybutadiene orpolyisoprene) through the residue X of a coupling agent. These studieshave confirmed that with n greater than or equal to 2 it is possible toachieve morphologies with spherical or cylindrical domains ofpolystyrene even at styrene contents exceeding 40% by weight. Becausethe B blocks in such materials cannot serve as bridges connecting glassypolystyrene domains, these polymers have little mechanical strength andpoor elastic recovery, and are thus unsuitable as elastomers.

BRIEF SUMMARY OF THE INVENTION

Applicants have now discovered that it is possible to obtain highmonoalkenyl arene content elastomers (from 40 to about 75% monoalkenylarene by weight) that possess spherical or cylindrical morphology, andare true elastomers, by controlling the structure and content of thepolymer arms in a particular manner without tapering or randomizingstyrene in the rubber block. Such polymers would be expected to be morethermally and/or mechanically stable than lower styrene contentelastomers and have a greater ability to blend with polystyrenehomopolymers.

A preferred embodiment of the present invention includes an elastomericpolymer composition comprising miktopolymers of the structure(A₂-B)_(n)—X-(A₁), where

-   -   a. A₁ and A₂ are each a polymer block of a monoalkenyl arene and        B is a polymer block of one or more conjugated dienes or a        hydrogenated polymer block of one or more conjugated dienes;    -   b. n is an integer from 2 to 30; and    -   c. X is the residue of a coupling agent;    -   and wherein:        -   i. τ is an asymmetry parameter of monoalkenyl arene            associated with the A₁ and A₂ blocks according to the            formula τ=NA₁/(NA₁+NA₂) where NA₁ is the number of monomer            units in the A₁ monoalkenyl arene block and NA₂ is the            number of monomer units in an A₂ monoalkenyl arene block;        -   ii. f is the volume fraction of monoalkenyl arene in said            miktopolymer;        -   iii. τ has a value of 0.7 to 0.95;        -   iv. f has a value greater than or equal to 0.4; and        -   v. block A₁ has a peak molecular weight of between 10,000            and 300,000, where the ratio of the peak molecular weight of            A₁ to A₂ is greater than or equal to 2.

According to another preferred embodiment of the present invention, anelastomeric polymer, wherein the mono alkenyl arene for the A₁ and A₂blocks is styrene and said conjugated diene for the B block is selectedfrom the group consisting of isoprene, 1,3-butadiene and mixturesthereof.

According to yet another preferred embodiment of the present invention,an elastomeric polymer includes at least 90% of the unsaturated bonds inthe B blocks of the polymer are hydrogenated and the conjugated diene is1,3-butadiene and wherein about 20 to about 80 mol percent of thecondensed butadiene units in block B have 1,2-configuration.

According to yet another preferred embodiment of the present invention,an elastomeric polymer, wherein the monoalkenyl arene content rangesfrom about 40 to about 75 weight percent for the block copolymer.

According to yet another preferred embodiment of the present invention,an elastomeric polymer includes the block A1 has a molecular weight ofbetween 10,000 and 300,000, said A2 block has a molecular weight ofbetween 5,000 and 30,000, and said block B has a molecular weight ofbetween 10,000 and 150,000.

According to yet another preferred embodiment of the present invention,an elastomeric polymer includes at least one component selected from thegroup consisting of fillers, reinforcements, polymer extending oils,tackifying resins, lubricants, stabilizers, styrene polymers,antioxidants, styrene/diene block copolymers and polyolefins.

According to yet another preferred embodiment of the present invention,an elastomeric polymer includes a process for preparing a miktopolymerof the structure (A₂-B)_(n)—X-(A₁), where

-   -   a. A₁ and A₂ are each a polymer block of a monoalkenyl arene and        B is a polymer block of one or more conjugated dienes or a        hydrogenated polymer block of one or more conjugated dienes;    -   b. n is an integer from 2 to 30;    -   c. X is the residue of a coupling agent;    -   d. τ is an asymmetry parameter of monoalkenyl arene associated        with the A₁ and A₂ blocks according to the formula        τ=NA₁/(NA₁+NA₂) where NA₁ is the number of monomer units in the        A₁ monoalkenyl arene block and NA₂ is the number of monomer        units in an A₂ monoalkenyl arene block;    -   e. f is the volume fraction of monoalkenyl arene in said        miktopolymer; said process comprising:        -   i. polymerizing a monoalkenyl arene in a first reactor in            the presence of an inert hydrocarbon solvent and an            organolithium initiator whereby a living polymer block A₂            terminated with a lithium ion is formed;        -   ii. adding a conjugated diene to the first reactor and            continuing the polymerization of the conjugated diene            whereby a living polymer block A₂B terminated with a lithium            ion is formed;        -   iii. polymerizing a monoalkenyl arene in a second reactor in            the presence of an inert hydrocarbon solvent and an            organolithium initiator whereby a living polymer block A₁            terminated with a lithium ion is formed; and        -   iv. combining the contents of the first reactor and second            reactor, and then adding a coupling agent, wherein said            miktopolymer is formed;        -   wherein the molecular weights of the A₁ and A₂ blocks and            the amount of A₂B blocks and A₁ blocks are controlled by            varying the relative amounts of said blocks and said            coupling agent to achieve a value for τ of 0.7 to 0.95 and a            value for f greater than or equal to 0.4.

According to yet another preferred embodiment of the present invention,a process wherein the mono alkenyl arene for the A1 and A2 blocks isstyrene and said conjugated diene for the B block is selected from thegroup consisting of isoprene, 1,3-butadiene and mixtures thereof.

According to yet another preferred embodiment of the present invention,a process wherein the conjugated diene is 1,3-butadiene and wherein lessthan about 15 mol percent of the condensed butadiene units in block Bhave 1,2-configuration.

According to yet another preferred embodiment of the present invention,a process wherein the monoalkenyl arene content ranges from about 40 toabout 75 weight percent for the block copolymer.

According to yet another preferred embodiment of the present invention,a process wherein the block A1 has a molecular weight of between 10,000and 300,000, said A2 block has a molecular weight of between 5,000 and30,000, and said block B has a molecular weight of between 20,000 and150,000.

According to yet another preferred embodiment of the present invention,the process includes at least one component selected from the groupconsisting of fillers, reinforcements, polymer extending oils,tackifying resins, lubricants, stabilizers, styrene polymers,antioxidants, styrene/diene block copolymers and polyolefins.

According to yet another preferred embodiment of the present invention,a process wherein the article is formed in a process selected from thegroup consisting of injection molding, over molding, dipping, extrusion,roto molding, slush molding, fiber spinning, film making or foaming.

According to yet another preferred embodiment of the present invention,a process wherein the article is selected from the group consisting ofclosures, synthetic corks, cap seals, tubing, food containers, beveragecontainers, interior automotive parts, window gaskets, elastic films,foamed products, gels, cushions, bicomponent fibers, monofilaments,adhesives, cosmetics and medical goods.

According to yet another preferred embodiment of the present invention,an elastomeric polymer composition comprising miktopolymers of thestructure (A₂-B₂)_(n)—X—(B₁-A₁), where

-   -   a. A₁ and A₂ are each a polymer block of a monoalkenyl arene and        B₁ and B₂ are polymer blocks of one or more conjugated dienes or        hydrogenated polymer blocks of one or more conjugated dienes;    -   b. n is an integer from 2 to 30; and    -   c. X is the residue of a coupling agent; and wherein:        -   i. τ is an asymmetry parameter of monoalkenyl arene            associated with the A₁ and A₂ blocks according to the            formula τ=NA₁/(NA₁+NA₂) where NA₁ is the number of monomer            units in the A₁ monoalkenyl arene block and NA₂ is the            number of monomer units in an A₂ monoalkenyl arene block;        -   ii. f is the volume fraction of monoalkenyl arene in said            miktopolymer;        -   iii. τ has a value of 0.7 to 0.95;        -   iv. f has a value greater than or equal to 0.4;        -   v. block A₁ has a peak molecular weight of between 10,000            and 300,000, and the ratio of the peak molecular weight of            A₁ to A₂ is greater than or equal to 2; and        -   vi. B₂ has a peak molecular weight of between 20,000 and            150,000 and B₁ has a peak molecular weight of between 200            and 5,000.

According to yet another preferred embodiment of the present invention,an elastomeric polymer composition wherein block A₁ has a molecularweight of between 10,000 and 300,000, said A₂ block has a molecularweight of between 5,000 and 30,000, said block B₂ has a molecular weightof between 20,000 and 100,000 and said block B₁ has a molecular weightof between 200 and 3,000.

According to yet another preferred embodiment of the present invention,an elastomeric polymer composition wherein n is an integer from 4 to 10.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated and described herein with referenceto the various drawings, in which like reference numbers denote likemethod steps and/or system components, respectively, and in which:

FIG. 1 illustrates the overall structure of the miktopolymers.

FIG. 2 illustrates a phase diagram of the possible miktopolymer that maybe prepared by the present invention.

FIG. 3 is a graph of tensile strength vs. elongation of various SEBS,SBS, and SIS polymers containing different amounts of polystyrene.

DETAILED DESCRIPTION OF THE INVENTION

In various exemplary embodiments, the present invention broadlycomprises a novel block copolymer composition or miktopolymer of thestructure (A₂-B)_(n)—X-(A₁), where

-   -   a. A₁ and A₂ are each a polymer block of a monoalkenyl arene and        B is a polymer block of one or more conjugated dienes or a        hydrogenated polymer block of one or more conjugated dienes;    -   b. n is an integer from 2 to 30; and    -   c. X is the residue of a coupling agent;    -   and wherein:        -   i. τ is an asymmetry parameter of monoalkenyl arene            associated with the A₁ and A₂ blocks according to the            formula τ−NA₁/(NA₁+NA₂) where NA₁ is the number of monomer            units in the A₁ monoalkenyl arene block and NA₂ is the            number of monomer units in an A₂ monoalkenyl arene block;        -   ii. f is the volume fraction of monoalkenyl arene in said            miktopolymer;        -   iii. τ has a value of 0.70 to 0.95;        -   iv. f has a value greater than or equal to 0.4; and        -   v. block A₁ has a peak molecular weight of between 10,000            and 300,000, where the ratio of the peak molecular weight of            A₁ to A₂ is greater than or equal to 2.

The particular compositions of the present invention are miktopolymersmeaning that they contain multiple arms that have at least two differentcompositions radiating from a central coupling site. In particular, atleast one arm comprises a monoalkenyl arene alone or with a very smalldiene block, while at least one other arm comprises a diblock of amonoalkenyl arene and a diene such as isoprene, butadiene, mixturesthereof and their hydrogenated analogues. It is important that the armconsisting essentially of monoalkenyl arene is different in molecularweight from the monoalkenyl arene block on the diene arm. Thisdifference in A block molecular weight, or asymmetry, can be describedby the parameter τ, where τ=NA₁/(NA₁+NA₂) where NA₁ is the number ofmonomer units in the A₁ monoalkenyl arene block and NA₂ is the number ofmonomer units in an A₂ monoalkenyl arene block. This structure is shownand described further in FIG. 1.

In another embodiment, the invention relates to an elastomeric polymercomposition comprising miktopolymers of the structure(A₂-B₂)_(n)—X—(B₁-A₁), where

-   -   a. A₁ and A₂ are each a polymer block of a monoalkenyl arene and        B₁ and B₂ are polymer blocks of one or more conjugated dienes or        a hydrogenated polymer block of one or more conjugated dienes    -   b. n is an integer from 2 to 30; and    -   c. X is the residue of a coupling agent;    -   and wherein:        -   i. τ is an asymmetry parameter of monoalkenyl arene            associated with the A₁ and A₂ blocks according to the            formula τ=NA₁/(NA₁+NA₂) where NA₁ is the number of monomer            units in the A₁ monoalkenyl arene block and NA₂ is the            number of monomer units in an A₂ monoalkenyl arene block;        -   ii. f is the volume fraction of monoalkenyl arene in said            miktopolymer;        -   iii. τ has a value of 0.7 to 0.95;        -   iv. f has a value greater than or equal to 0.4;        -   v. block A₁ has a peak molecular weight of between 10,000            and 300,000, and the ratio of the peak molecular weight of            A₁ to A₂ is greater than or equal to 2; and        -   vi. B₂ has a peak molecular weight of between 20,000 and            150,000 and B₁ has a peak molecular weight of between 200            and 5,000.

In still another embodiment, the invention relates to a process forpreparing a miktopolymer of the structure (A₂-B)_(n)—X-(A₁), where:

-   -   a. A₁ and A₂ are each a polymer block of a monoalkenyl arene and        B is a polymer block of one or more conjugated dienes or a        hydrogenated polymer block of one or more conjugated dienes;    -   b. n is an integer from 2 to 30;    -   c. X is the residue of a coupling agent;    -   d. τ is an asymmetry parameter of monoalkenyl arene associated        with the A₁ and A₂ blocks according to the formula        τ=NA₁/(NA₁+NA₂) where NA₁ is the number of monomer units in the        A₁ monoalkenyl arene block and NA₂ is the number of monomer        units in an A₂ monoalkenyl arene block; and    -   e. f is the volume fraction of monoalkenyl arene in said        miktopolymer; said process comprising:        -   i. polymerizing a monoalkenyl arene in a first reactor in            the presence of an inert hydrocarbon solvent and an            organolithium initiator whereby a living polymer block A₂            terminated with a lithium ion is formed;        -   ii. adding a conjugated diene to the first reactor and            continuing the polymerization of the conjugated diene            whereby a living polymer block A₂B terminated with a lithium            ion is formed;        -   iii. polymerizing a monoalkenyl arene in a second reactor in            the presence of an inert hydrocarbon solvent and an            organolithium initiator whereby a living polymer block A₁            terminated with a lithium ion is formed; and        -   iv. combining the contents of the first reactor and second            reactor, and then adding a coupling agent, wherein said            miktopolymer is formed;        -   wherein the A₁ and A₂ molecular weights and the amount of            A₂B blocks and A₁ blocks are controlled by varying the            relative amounts of said blocks and said coupling agent to            achieve a value for τ of 0.7 to 0.95 and a value for f            greater than or equal to 0.4.

The diene blocks of the miktopolymers produced by steps i-iv can besaturated by catalytic hydrogenation to produce “saturated”miktopolymers. Additionally, the diene blocks of the miktopolymersproduced by steps i-iv may be “partially hydrogenated.”

The term “miktopolymers” refers to a composition that contains arms ofdistinctly different compositions in contrast to the relatively commonradial or star polymers in which all arms are essentially the same andthe only variation is the number of arms.

FIG. 2

FIG. 2 illustrates a phase diagram of the possible miktopolymers thatcan be prepared by the present invention as described above. The diagramshows the expected phase boundary between the cylindrical morphology andthe lamellar morphology in the coordinates of τ and f. Three phaseboundaries are shown in FIG. 2, corresponding to cases of a miktopolymerwith 3 arms (n=2, squares), 4 arms (n=3, circles), and 6 arms (n=5,triangles). The figure shows a pronounced deflection of thecylinder-lamellar phase boundary to values of f greatly exceeding 0.4when τ is restricted to the range of approximately 0.7 to 0.95 (shaded).This deflection of the phase boundary to unusually large values of f isespecially pronounced as n is increased to 5.

As shown in the examples that follow, compositions of the presentinvention will have elastomeric properties along with much improvedstability. Of primary interest, it will be possible to obtainsignificant and unexpected property advantages in end uses such aspackaging, films, fiber, personal hygiene, soft compounds, andcompatibilizing agents. Details regarding the particular miktopolymer,along with the processes for making them are described further below.

The block copolymers utilized in the present invention broadly comprisepolymers of styrene/diene diblock copolymer arms and styrene homopolymerarms in a particular configuration that has a unique set of propertyadvantages. One important aspect of the block copolymers used inpreparing the compositions of the present invention is the monoalkenylarene content. As noted hereinbefore, the monoalkenyl arene contentshould be equal to or greater than 40 weight percent, based on the totalweight of the block copolymer. Preferably the monoalkenyl arene contentwill range from about 40 to about 75 weight percent for the blockcopolymer.

The monoalkenyl arenes utilized in the A1 and A2 blocks of the blockcopolymers are independently selected from styrene, alpha-methylstyrene,para-methylstyrene, vinyl toluene, vinylnaphthalene, diphenyl ethyleneand para-butyl styrene or mixtures thereof. Of these, styrene is themost preferred.

The conjugated dienes of the B and B1 blocks are independently selectedfrom 1,3-butadiene and substituted butadienes, such as, for example,isoprene, piperylene, 2,3-dimethyl-1,3-butadiene, and1-phenyl-1,3-butadiene, or mixtures thereof. Of these, isoprene and1,3-butadiene are the most preferred with 1,3-butadiene being the morepreferred of the two. When a small B1 block is used, it is muchpreferred that the conjugated diene is 1,3-butadiene.

Optionally, the B, B1, and B2 blocks of the synthesized miktopolymerscan be saturated by catalytic hydrogenation. Such polymers are termed“saturated” or “hydrogenated” miktopolymers. When butadiene blocks arehydrogenated it is preferred that their 1,2 content be between 20 and85% by weight.

While a wide range of molecular weights of the block copolymers utilizedin the present invention can be used, in many instances the peakmolecular weight of each A1 block will independently range from about10,000 to about 300,000, preferably from about 20,000 to about 200,000,the peak molecular weight of each A2 block will independently rangebetween 5,000 and 30,000, and the peak molecular weight of each B and B2block will independently range from about 10,000 to about 150,000,preferably from about 20,000 to about 100,000, for the coupled blockcopolymers. The block copolymers of the present invention may beprepared by any of the methods known in the art, including couplingusing standard coupling agents.

Preparation of radial (branched) polymers, including miktopolymers andstar polymers, requires a post-polymerization step called “coupling”. Itis possible to have either a branched selectively hydrogenated blockcopolymer and/or a branched tailored softening modifier. In the aboveradial formula for the selectively hydrogenated block copolymer, n is aninteger of from 2 to about 30, preferably from about 4 to about 10, andX is the remnant or residue of a coupling agent. A variety of couplingagents are known in the art and include, for example, dihalo alkanes,silicon halides, siloxanes, multifunctional epoxides, silica compounds,esters of monohydric alcohols with carboxylic acids, (e.g. dimethyladipate) and epoxidized oils. Star-shaped polymers are prepared withpolyalkenyl coupling agents as disclosed in, for example, U.S. Pat. Nos.3,985,830; 4,391,949; and 4,444,953; Canadian Patent Number 716,645.Suitable polyalkenyl coupling agents include divinylbenzene, andpreferably m-divinylbenzene. Preferred are tetra-alkoxysilanes such astetra-ethoxysilane (TEOS) and tetra-methoxysilane,alkyl-trialkoxysilanes such as methyl-trimethoxy silane (MTMS),aliphatic diesters such as dimethyl adipate and diethyl adipate, anddiglycidyl aromatic epoxy compounds such as diglycidyl ethers derivingfrom the reaction of bis-phenol A and epichlorohydrin.

Coupling efficiency is of critical importance in the synthesis of blockcopolymers, in which the copolymers are prepared by a linkingtechnology. In a typical anionic polymer synthesis, prior to thecoupling reaction, the unlinked arm has only one hard segment (typicallypolystyrene). Two hard segments are required in the block copolymer ifit is to contribute to the strength mechanism of the material. Uncoupledarms dilute the strength forming network of a block copolymer thatweakens the material. The very high coupling efficiency realized in thepresent invention is key to making high strength, coupled, blockcopolymers.

As used herein, the term “molecular weights” refers to the truemolecular weight in g/mol of the polymer or block of the copolymer. Themolecular weights referred to in this specification and claims can bemeasured with gel permeation chromatography (GPC) using polystyrenecalibration standards, such as is done according to ASTM 3536. GPC is awell-known method wherein polymers are separated according to molecularsize, the largest molecule eluting first. The chromatograph iscalibrated using commercially available polystyrene molecular weightstandards. The molecular weight of polymers measured using GPC socalibrated are styrene equivalent molecular weights. The styreneequivalent molecular weight may be converted to true molecular weightwhen the styrene content of the polymer and the vinyl content of thediene segments are known. The detector used is preferably a combinationultraviolet and refractive index detector. The molecular weightsexpressed herein are measured at the peak of the GPC trace, converted totrue molecular weights, and are commonly referred to as “peak molecularweights”.

As noted hereinbefore, the block copolymers used in the presentinvention have at least two A2 blocks and at least one A1 block. In thecoupling process to make the miktopolymers, there will be otherstructures that are created. However, those structures will becompatible with the desired structure claimed. For example while asingle structure such as (A2-B)4-X-(A1) would be ideal, it will berecognized by one skilled in the art that most coupling processes willyield a mixture of (A2-B)1-X-(A1), (A2-B)2-X-(A1), (A2-B)3-X-(A1) andthe like. Since the diblock arms A2-B and the block arm A1 are nearlythe same length for each of these structures, they can all beaccommodated in the same morphology. Thus, mixtures of the numbers ofarms will also perform as stable, high styrene content elastomers.

Anionic, solution co-polymerization to form the block copolymers of thepresent invention can be carried out using, to a great extent, known andpreviously employed methods and materials. In general, theco-polymerization is attained anionically, using known selections ofadjunct materials, including polymerization initiators, solvents,promoters, and structure modifiers.

One aspect of the present invention is to control the microstructure orvinyl content of the conjugated diene in the diene block. The term“vinyl content” refers to the fact that a conjugated diene ispolymerized via 1,2-addition (in the case of butadiene—it would be3,4-addition in the case of isoprene). Although a pure “vinyl” group isformed only in the case of 1,2-addition polymerization of 1,3-butadiene,the effects of 3,4-addition polymerization of isoprene (and similaraddition for other conjugated dienes) on the final properties of theblock copolymer will be similar. The term “vinyl” refers to the presenceof a pendant vinyl group on the polymer chain. When referring to the useof butadiene as the conjugated diene, it is preferred that less than 15mole percent of the repeat units have 1,2 vinyl configuration.Alternately if the polymer is to be hydrogenated it is preferred thatabout 20 to about 85 mol percent of the condensed butadiene units in thecopolymer block have 1,2 vinyl configuration as determined by proton NMRanalysis.

The solvent used as the polymerization vehicle may be any hydrocarbonthat does not react with the living anionic chain end of the formingpolymer, is easily handled in commercial polymerization units, andoffers the appropriate solubility characteristics for the productpolymer. For example, non-polar aliphatic hydrocarbons, which aregenerally lacking in ionizable hydrogens make particularly suitablesolvents. Frequently used are cyclic alkanes, such as cyclopentane,cyclohexane, cycloheptane, and cyclooctane, all of which are relativelynon-polar. Other suitable solvents will be known to one skilled in theart and can be selected to perform effectively in a given set of processconditions, with temperature being one of the major factors taken intoconsideration.

Starting materials for preparing the block copolymers and softeningmodifiers of the present invention include the initial monomers. Thealkenyl arene can be selected from styrene, alpha-methylstyrene,para-methylstyrene, vinyl toluene, vinylnaphthalene, diphenyl ethylene,and para-butyl styrene or mixtures thereof. Of these, styrene is mostpreferred and is commercially available, and relatively inexpensive,from a variety of manufacturers.

The conjugated dienes for use herein are 1,3-butadiene and substitutedbutadienes such as isoprene, piperylene, 2,3-dimethyl-1,3-butadiene, and1-phenyl-1,3-butadiene, or mixtures thereof. Of these, 1,3-butadiene ismost preferred. As used herein, and in the claims, “butadiene” refersspecifically to “1,3-butadiene”.

Other important starting materials for anionic co-polymerizationsinclude one or more polymerization initiators. In the present inventionsuch include, for example, alkyl lithium compounds and otherorganolithium compounds such as s-butyllithium, n-butyllithium,t-butyllithium, amyllithium and the like. Of the various polymerizationinitiators, s-butyllithium is preferred. The initiator can be used inthe polymerization mixture (including monomers and solvent) in an amountcalculated on the basis of one initiator molecule per desired polymerchain. The lithium initiator process is well known and is described in,for example, U.S. Pat. Nos. 4,039,593 and Re. 27,145, which descriptionsare incorporated herein by reference.

Polymerization conditions to prepare the novel copolymers of the presentinvention are typically similar to those used for anionicpolymerizations in general. In the present invention polymerization ispreferably carried out at a temperature of from about −30° C. to about150° C., more preferably about 10° C. to about 100° C., and mostpreferably, in view of industrial limitations, about 30° C. to about 90°C. It is carried out in an inert atmosphere preferably nitrogen, and mayalso be accomplished under pressure within the range of from about 0.5to about 10 bars. This copolymerization generally requires less thanabout 12 hours, and can be accomplished in from about 5 minutes to about5 hours, depending upon the temperature, the concentration of themonomer components, the molecular weight of the polymer and the amountof distribution agent that is employed.

The preferred process to prepare the polymer compositions of the presentinvention is to polymerize the A₂-B or A₂-B₂ arms of the block copolymerin a separate reactor from the A₁ or A₁-B, arms. The followingalternatives are thus possible:

-   -   a) In one process scenario, the following steps could be used:        -   i. polymerizing a monoalkenyl arene in a first reactor in            the presence of an inert hydrocarbon solvent and an            organolithium initiator whereby a living polymer block A₂            terminated with a lithium ion is formed;        -   ii. adding a conjugated diene to the first reactor and            continuing the polymerization of the conjugated diene            whereby a living polymer block A₂B terminated with a lithium            ion is formed;        -   iii. polymerizing a monoalkenyl arene in a second reactor in            the presence of an inert hydrocarbon solvent and an            organolithium initiator whereby a living polymer block A₁            terminated with a lithium ion is formed; and        -   iv. combining the contents of the first reactor and second            reactor, and then adding a coupling agent, wherein said            miktopolymer is formed;        -   wherein the amount of A₂B blocks and A₁ blocks are            controlled by varying the relative amounts of said blocks            and said coupling agent to achieve a value for τ of 0.7 to            0.95 and a value for f greater than or equal to 0.4.    -   b) In a second scenario, one could polymerize an additional        small B₁ block after the polymerization of the monoalkenyl arene        homopolymer block A₁. This will increase the rate of coupling.    -   c) Alternately, after the coupling agent is added to the living        A₁ block and after time for reaction, the A₂B arms could be        added. This assures that each coupling site has at least one A₁        block.    -   d) Alternately, after the coupling agent is added to the living        A₂B living diblock and after time for reaction, the A₁ blocks        could be added. This assures that each coupling site has at        least one A₂B diblock.

Alternatively, after the coupling step iv, the miktopolymers producedcould be catalytically hydrogenated to saturate the B, B₁, and B₂blocks. Hydrogenation can be carried out via any of the severalhydrogenation or selective hydrogenation processes known in the priorart. For example, such hydrogenation has been accomplished using methodssuch as those taught in, for example, U.S. Pat. Nos. 3,494,942;3,634,594; 3,670,054; 3,700,633; and Re. 27,145. Hydrogenation can becarried out under such conditions that at least about 90 percent of theconjugated diene double bonds have been reduced, and between zero and 10percent of the arene double bonds have been reduced. Preferred rangesare at least about 95 percent of the conjugated diene double bondsreduced, and more preferably about 98 percent of the conjugated dienedouble bonds are reduced. Alternatively, it is possible to hydrogenatethe polymer such that aromatic unsaturation is also reduced beyond the10 percent level mentioned above. In that case, the double bonds of boththe conjugated diene and arene may be reduced by 90 percent or more.

The last step, following all polymerization(s) and, optionally,hydrogenation, is a finishing treatment to remove the final polymersfrom the solvent. Various means and methods are known to those skilledin the art, and include use of steam to evaporate the solvent, andcoagulation of the polymer followed by filtration. The final result is a“clean” block copolymer composition useful for a wide variety ofchallenging applications, according to the properties thereof.

The polymer compositions of the present invention, by virtue of theirimproved thermal or mechanical stability and compatibility withpolystyrenes, are useful in a wide variety of applications. Thefollowing is a partial list of the many potential end uses orapplications: over molding, personal hygiene, molded and extruded goods,barrier films, packaging, closures such as synthetic corks and capseals, tubing, containers including containers for food or beverages,interior automotive applications, window gaskets, foamed products,elastic film, fibers including bicomponent and monofilament, adhesives,cosmetics and medical goods. In combination with oils the polymercompositions of the present invention can be made into gels for candles,personal care items, medical devices such as soft supports, cushions,pads and the like.

Finally, the copolymer compositions of the present invention can becompounded with other components not adversely affecting the copolymerproperties. Exemplary materials that could be used as additionalcomponents would include, without limitation, pigments, antioxidants,stabilizers, surfactants, waxes, flow promoters, traditional processingoils, solvents, particulates, tackifying resins, end block resins, andmaterials added to enhance processability and pellet handling of thecomposition. In addition, the copolymer compositions can be furtherformulated with other polymers, including by way of illustration and notlimitation, polyolefins (e.g., crystal polystyrene, propylenehomopolymers and copolymers, ethylene homopolymers and copolymers andbutylene homopolymers and copolymers), styrene polymers (e.g.,polystyrene homopolymers, HIPS, ABS, SAN), engineering thermoplastics,polyurethanes, polyphenylene oxides, polyamides, polycarbonates,polyesters, functionalized polymers (e.g., maleated PP, maleatedS-EB-S), styrene diene block copolymers (e.g. S—I—S, S—B—S, S—I/B—S),hydrogenated styrene diene block copolymers (e.g. S-EB-S, S-EP-S, S-EP,S-EB) and the like.

Tackifying resins include polystyrene block compatible resins andmidblock compatible resins. The polystyrene block compatible resin maybe selected from the group of coumarone-indene resin, polyindene resin,poly(methyl indene) resin, polystyrene resin,vinyltoluene-alphamethylstyrene resin, alphamethylstyrene resin andpolyphenylene ether, in particular poly(2,6-dimethyl-1,4-phenyleneether). Such resins are e.g. sold under the trademarks “HERCURES”,“ENDEX”, “KRISTALEX”, “NEVCHEM” and “PICCOTEX”. Resins compatible withthe hydrogenated (mid) block may be selected from the group consistingof compatible C5 hydrocarbon resins, hydrogenated C5 hydrocarbon resins,styrenated C5 resins, C5/C9 resins, styrenated terpene resins, fullyhydrogenated or partially hydrogenated C9 hydrocarbon resins, rosinsesters, rosins derivatives and mixtures thereof. These resins are e.g.sold under the trademarks “REGALITE”, “REGALREZ”, “ESCOREZ” and “ARKON.The amount of tackifying resin employed varies from about 5 to about 100parts by weight per hundred parts by weight rubber, or block copolymer,preferably about 20 to about 50 parts by weight. Also, one may use botha polystyrene block compatible resin and a midblock compatible resin.

Useful waxes may include petroleum waxes, both paraffin andmicrocrystalline, such as the SHELLWAX and SHELLMAX waxes from Shell,synthetic waxes, low molecular weight polyethylene and polypropylene,and naturally occurring waxes.

Examples of waxes that can be treated by the invention are paraffinwaxes and paraffin wax blends, preferably SPO, LMO, MMO and BSO waxes.

The process can be equally applied to synthetic waxes, such asFischer-Tropsch (FT) waxes. Said FT waxes are hydrocarbon waxes that areproduced by the reaction of carbon monoxide and hydrogen in the presenceof a catalyst.

Suitable waxes are mainly low molecular weight polyethylenes. Suitablegrades are e.g. supplied by Allied under the AC trade name, by QuantumChemical under the Petrothene trade name and by Eastman ChemicalProducts under the Epolene trade name.

The polymer blends of the present invention may be compounded furtherwith other polymers, oils, fillers, reinforcements, antioxidants,stabilizers, fire retardants, antiblocking agents, lubricants and otherrubber and plastic compounding ingredients without departing from thescope of this invention. Blends with 60 wt. % or more polystyrene are ofparticular interest because they are transparent and tough compared withtraditional block polymer/polystyrene blends.

EXAMPLES

The following examples are intended to be illustrative only, and are notintended to be, nor should they be construed as being, limitative in anyway of the scope of the present invention.

Example 1

The following describes the general procedure for the synthesis of the(A₂-B₂)_(n)—X-(A₁) block copolymer described above.

An appropriate amount of cyclohexane (purified with Alcoa alumina) wascharged to a 10 L stainless steel reactor vessel (1) and heated to 50°C. A calculated amount of sec-butyl lithium was charged, immediatelyfollowed by an amount of purified and stripped styrene. After a reactiontime a calculated second charge of styrene was dosed to obtain apredetermined target A₁ block molecular weight. After styrenepolymerization one molar equivalent to polystyrene-lithium oftetramethoxysilane was added.

A second stainless steel reactor vessel (2.3 L) was charged with anappropriate amount of cyclohexane (purified with Alcoa alumina) andheated to 50° C., a calculated amount of sec-butyl lithium which wastwice the amount used to make the styrene block in reactor 1 wascharged, immediately followed by an amount of purified and strippedstyrene. After a reaction time a calculated second charge of styrene wasdosed to obtain a predetermined A2 target molecular weight. Afterstyrene polymerization a calculated amount of purified diene was addedto the reactor at 70° C. After butadiene polymerization to form the A2 Bdiblock, the reaction mixture of reactor 1 was added to that of reactor2 and allowed to react for at least 10 minutes before the polymer cementwas sampled.

The samples were taken such that the tensile properties, cyclichysteresis to 100% extension, and cyclic hysteresis to 300% extension,and the molecular weight of the A1, A2, and B molecular weights could bedetermined. The results of the testing are displayed below in Table 1.

TABLE 1 Results from Example 1 Polymer Tensile Strength, psi 3188Elongation, % 817 Modulus 100%, psi 351 Modulus 300%, psi 730 Modulus500%, psi 1369 Stress at 100% extension, psi 301 Recoverable Energyafter 1 cycle, % 79 Hysteresis set @ 1 cycle, % 6 Stress @ 50% Ext.2^(nd) Unld, psi 184 Stress at 300% extension, psi 472 RecoverableEnergy after 1 cycle, % 73 Hysteresis set @ 1 cycle, % 14 Stress @ 50%Ext. 2^(nd) Unld, psi 122 A1 molecular weight 45,550 gm/mole A2molecular weight 10,200 gm/mole B molecular weight 52,300 gm/mole τ =NA₁/(NA₁ + NA₂) 45,550/(45,500 + 10,200) = 0.818

Prophetic Examples Example 2

The following describes the (A₂-B)₂—X-(A₁) block copolymer describedabove.

The targets of a prophetic block copolymer composition have been listedin Table 2 obtained by the method of Example 1. See paragraphs [0066],[0067], and [0068].

TABLE 2 Target polymer A₁ Polystyrene molecular weight 47,000 gm/moleCoupling agent Tetramethoxysilane A₂ polystyrene molecular weight 10,000gm/mole A₂ B Molecular Weight 60,000 gm/mole Polystyrene content PSC(wt. %) 40% τ = NA₁/(NA₁ + NA₂) 47,000/(47,000 + 10,000) = 0.825

Example 3

The following describes the general procedure for the synthesis of the(A₂-B₂)₂—X—(B₁A1) block copolymer described above.

An appropriate amount of cyclohexane (purified with Alcoa alumina) wascharged to a 10 L stainless steel reactor vessel (1) and heated to 50°C. A calculated amount of sec-butyl lithium was charged, immediatelyfollowed by an amount of purified and stripped styrene. After a reactiontime a calculated second charge of styrene was dosed to obtain apredetermined target A₁ block molecular weight. After styrenepolymerization a small amount of purified butadiene was added to thereactor in order to add a small B₁ block of approximately 500 g/mole andform the A₁B₁ diblocks. Subsequent to the butadiene addition, one molarequivalent to polystyrene-lithium of tetramethoxysilane was added to thereactor.

A second stainless steel reactor vessel was charged with an appropriateamount of cyclohexane (purified with Alcoa alumina) and heated to 50° C.A calculated amount of sec-butyl lithium (twice the amount used to makethe A₁B1 diblocks in reactor 1) was charged, immediately followed by anamount of purified and stripped styrene. After a reaction time acalculated second charge of styrene was dosed to obtain a predeterminedA₂ target molecular weight. After styrene polymerization, a calculatedamount of purified diene was added to the reactor at 70° C. Afterbutadiene polymerization to form the A₂B₂ diblock, the reactor mixtureof reactor 1 was added to that of reactor 2 and allowed to react for atleast 10 minutes before the polymer cement was sampled.

B1 was only enough to terminate the polystyrene block polymer (about 500gm/mole) of butadiene.

The contents of reactor 1 and reactor 2 were combined and coupled withtetramethoxysilane.

TABLE 3 Target polymer A₁ Polystyrene molecular weight 47,000 gm/moleCoupling agent Tetramethoxysilane A₂ polystyrene molecular weight 10,000gm/mole A₂ B₂ Molecular weight 60,000 gm/mole Polystyrene content PSC(wt. %) About 40% τ = NA₁/(NA₁ + NA₂) 47,000/(47,000 + 10,000) = 0.825B₂ polybutadiene molecular weight about 500 g/mole

Comparative Example Example 4

Comparative example 4 consists of a SBS block copolymer having apolystyrene content of 40% by weight. Styrene-butadiene-styrene triblockcopolymers can be produced by anionic synthesis where styrene monomer isadded to a lithium initiator producing polystyrene. Near the end of thepolymerization of the polystyrene, butadiene monomer is added. After thebutadiene has almost completely polymerized, more styrene monomer isadded, thereby forming the SBS triblock. The amounts of styrene andbutadiene and reactor times can be varied in order to make blockcopolymers that have a small amount (10 weight percent) of styrene up toa large amount of polystyrene (up to about 40 wt. %). Likewise the SBScan contain a small amount of butadiene or a large amount.

Styrene-butadiene-styrene triblock copolymers can also be made bycoupling. Such copolymers can be produced by anionic synthesis wherestyrene monomer is added to a lithium initiator producing polystyrene.Near the end of the polymerization of the polystyrene, butadiene monomeris added. After the butadiene has almost completely polymerized, acoupling agent is added to produce an (S—B)_(n) block copolymer. When nequals 2, the result is the triblock SBS, where two diblocks of SBcouple to one another via their butadiene blocks. Coupled SBS is sold inthe market place under the name Kraton® D1101 or 1102. It is easier toprecisely control the molecular size of each block and at a fasterproduction rate with coupled SBS as compared to linear sequentiallyproduced SBS.

FIG. 3, it shows mechanical test data for SIS, SBS, and SEBS blockcopolymers containing various percentages of polystyrene. While thelower percentage of polystyrene block copolymer are very elastic innature as indicated by high elongation percentages, the high contentpolystyrene block copolymer illustrates a very plastic nature.Specifically, the SBS that has 40% polystyrene exhibits a yield stressupon tensile elongation which indicates the plastic nature of thiscomparative example.

Although the present invention has been illustrated and described hereinwith reference to preferred embodiments and specific examples thereof,it will be readily apparent to those of ordinary skill in the art thatother embodiments and examples may perform similar functions and/orachieve like results. All such equivalent embodiments and examples arewithin the spirit and scope of the present invention and are intended tobe covered by the following claims.

1. An elastomeric polymer composition comprising miktopolymers of thestructure (A₂-B)_(n)—X-(A₁), where a. A₁ and A₂ are each a polymer blockof a monoalkenyl arene and B is a polymer block of one or moreconjugated dienes or a hydrogenated polymer block of one or moreconjugated dienes; b. n is an integer from 2 to 30; and c. X is theresidue of a coupling agent; and wherein: i. τ is an asymmetry parameterof monoalkenyl arene associated with the A₁ and A₂ blocks according tothe formula τ=NA₁/(NA₁+NA₂) where NA₁ is the number of monomer units inthe A₁ monoalkenyl arene block and NA₂ is the number of monomer units inan A₂ monoalkenyl arene block; ii. f is the volume fraction ofmonoalkenyl arene in said miktopolymer; iii. τ has a value of 0.7 to0.95; iv. f has a value greater than or equal to 0.4; and v. block A₁has a peak molecular weight of between 10,000 and 300,000, where theratio of the peak molecular weight of A₁ to A₂ is greater than or equalto
 2. 2. The composition according to claim 1, wherein said monoalkenylarene for the A₁ and A₂ blocks is styrene and said conjugated diene forthe B block is selected from the group consisting of isoprene,1,3-butadiene and mixtures thereof.
 3. The composition according toclaim 2, wherein at least 90% of the unsaturated bonds in the B blocksof the polymer are hydrogenated and the conjugated diene is1,3-butadiene and wherein about 20 to about 80 mol percent of thecondensed butadiene units in block B have 1,2-configuration.
 4. Thecomposition according to claim 2, wherein the monoalkenyl arene contentranges from about 40 to about 75 weight percent of said miktopolymer. 5.The composition according to claim 1, wherein said block A₁ has a peakmolecular weight of between 10,000 and 300,000, said A₂ block has a peakmolecular weight of between 5,000 and 30,000, and said block B has apeak molecular weight of between 10,000 and 150,000.
 6. A compositionaccording to claim 1 and comprising at least one component selected fromthe group consisting of fillers, reinforcements, polymer extending oils,tackifying resins, lubricants, stabilizers, styrene polymers,antioxidants, styrene/diene block copolymers and polyolefins.
 7. Acomposition according to claim 1, wherein the composition iscatalytically hydrogenated and at least about 90 percent of theconjugated diene double bonds have been reduced and between 0 to about10 percent of the arene double bonds have been reduced.
 8. A process forpreparing a miktopolymer of the structure (A₂-B)_(n)—X-(A₁), where a. A₁and A₂ are each a polymer block of a monoalkenyl arene and B is apolymer block of one or more conjugated dienes or a hydrogenated polymerblock of one or more conjugated dienes; b. n is an integer from 2 to 30;c. X is the residue of a coupling agent; d. τ is an asymmetry parameterof monoalkenyl arene associated with the A₁ and A₂ blocks according tothe formula τ=NA₁/(NA₁+NA₂) where NA_(I) is the number of monomer unitsin the A₁ monoalkenyl arene block and NA₂ is the number of monomer unitsin an A₂ monoalkenyl arene block; e. f is the volume fraction ofmonoalkenyl arene in said miktopolymer; said process comprising: i.polymerizing a monoalkenyl arene in a first reactor in the presence ofan inert hydrocarbon solvent and an organolithium initiator whereby aliving polymer block A₂ terminated with a lithium ion is formed; ii.adding a conjugated diene to the first reactor and continuing thepolymerization of the conjugated diene whereby a living polymer blockA₂B terminated with a lithium ion is formed; iii. polymerizing amonoalkenyl arene in a second reactor in the presence of an inerthydrocarbon solvent and an organolithium initiator whereby a livingpolymer block A₁ terminated with a lithium ion is formed; and iv.combining the contents of the first reactor and second reactor, and thenadding a coupling agent, wherein said miktopolymer is formed; whereinthe molecular weights of the A₁ and A₂ blocks and the amount of A₂Bblocks and A₁ blocks are controlled to achieve a value for τ of 0.7 to0.95 and a value for f greater than or equal to 0.4.
 9. The processaccording to claim 8, wherein said mono alkenyl arene for the A₁ and A₂blocks is styrene and said conjugated diene for the B block is selectedfrom the group consisting of isoprene, 1,3-butadiene and mixturesthereof.
 10. The process according to claim 9, wherein said conjugateddiene is 1,3-butadiene and wherein less than about 15 mol percent of thecondensed butadiene units in block B have 1,2-configuration.
 11. Theprocess according to claim 10, wherein the monoalkenyl arene contentranges from about 40 to about 75 weight percent for the miktopolymer.12. The process according to claim 11, wherein said block A₁ has a peakmolecular weight of between 10,000 and 300,000, said A₂ block has a peakmolecular weight of between 5,000 and 30,000, and said block B has apeak molecular weight of between 20,000 and 150,000.
 13. A processaccording to claim 8, wherein n is an integer from 4 to
 10. 14. Theprocess of claim 8, wherein an article is formed in a process selectedfrom the group consisting of injection molding, over molding, dipping,extrusion, roto molding, slush molding, fiber spinning, film making orfoaming.
 15. The process of claim 14, wherein an article is selectedfrom the group consisting of closures, synthetic corks, cap seals,tubing, food containers, beverage containers, interior automotive parts,window gaskets, elastic films, foamed products, gels, cushions,bicomponent fibers, monofilaments, adhesives, cosmetics and medicalgoods.
 16. The process according to claim 8, wherein the miktopolymer iscatalytically hydrogenated and at least about 90 percent of theconjugated diene double bonds have been reduced and between 0 to about10 percent of the arene double bonds have been reduced.